Burner control system



' Feb. 6, 1945.

C. B. SPANGENBERG ETAL BURNER CONTROL SYSTEM Filed Dec. 1:5, 1941 szFig. 2.

aha-71!- pauganlocrg .A-fihuv Swanson... i3! INVENTORS T BY M when thereis no flame at the burner.

Patented Feb. 6, 1945 BURNER CONTROL SYSTEM Charles B. Spangenberg and-Arthur H. Swanson, Philadelphia, Pa... 'assignors toMinneapolis-Hon'eywell Regulator Company, Minneapolis, Minn., acorporation of Delaware Application December 13, 1941, Serial No.422,818

12 Claims.

This invention relates generally to fluid fuel burner control systems.

In a conventional oil burner control system, there is customarilyprovided some means responsive to the presence of flame at the burner,which means must be maintained in an operative condition in order topermit the supply of fuel to the burner. Many types of flame responsivemeans are well known in the art, for example temperature responsivestack switches, photocells, flame electrodes which provide a conductivepath through the flame, etc. These flame responsive devices areordinarily maintained conductive due to the heat of the flame, the lightproduced by the flame, or the conductivity of the flame itself. Inconventional systems, when the flame responsive device is conductive,indicating the presence of flame at the burner, the feeding of fuel tothe burner is allowed to continue if demanded by the "room thermostat,or other main control device.

In order to start a burner with a control system employing such a flameresponsive device, some means must be provided for permitting the supplyof fuel during the starting period Such the appended claims, in which,

-Figure 1 represents a circuit diagram of a control system embodying ourinvention, and

Figure 2 is a modification of the control, sysspeciflcation,- anddrawing,

tem of Figure 1, embodying our invention in a somewhat different form.

v k Figure .1

Referring to Figure 1, It! represents a motor driving means forsupplying fuel to a fluid fuel burner (not shown). An ignition device His provided for igniting the fuel asit issues from the burner. Motor l0and igniter II are adapted to be energized from a pair of power supplylines 12 and I3.

and I3 is a transformer 14 having a primary means ordinarily consists ofa timing device, 7

which allows the feeding of fuel to the burner after a call for heat bythe main control, regardless of the flame responsive device. If theflame responsive means does not respond during the starting period, thesupply of fuel to the burner is cut off by the timing device at the endof a predetermined time. i

An object of the present inventionis to provide an improved andsimplified burner control system, including a novel means of timing thedura tion of the starting period.

Another object of the present invention is to provide an improved burnercontrol system including an electric discharge device, wherein thecontrolling devices are connected in the input circuit of the dischargedevice, so'that the current carried by the controlling devices is at a'A further object of the present invention is to construct a burnercontrol system wherein the ceeds a predetermined value.

comprises a glass tube 26 having a pair of electiming of the startingperiod is regulated by a v v condenser connected in the input circuit ofan winding l5 and. a pair of secondary windings I6 I and 11 Operation ofthe burner motor lfl is controlled by a thermostatic device 20 whichmay-be a room thermostat mounted in the space to be heated by theburner. The thermostat 211.comprises a bimetallic elementjl, whichcarries on its free end a contact arm 22, which on a decrease intemperature to a" predetermined point is adapted to engage a stationarycontact 23. A permanent magnet 24 is mounted adjacent the stationarycontact 23 to provide a snap actionheating /system, isprovided to shutdown the.

system in case the said limiting condition ex- The switch 25 trodes 2!and 28 in one end thereof, and a pool of mercury 29 which is adapted toroll along the bottom of the tube and make and break the circuit betweenthe electrodes as the tube is shifted back and forth by a suitablecondition responsive element (not shown).

A combustion responsive switch 33 comprises a movable contact arm 34 anda stationary contact 35.

This switch may be of the usual slip friction type which is actuated bymeans of a thermal element responsive to the stack temperature or thetemperature in the combustion chamber of the furnace. Due to the slipfriction action between the thermal element and the switch arm, theswitch is responsive to a change in temperature rather than to anypredetermined temperature.

The thermostat 20, the limit switch 25, and the Also connected to thepower lines I2 I clarity.

46 whose energization controls the operationof a, switch arm 41 into andout of engagement with the stationary switch contact 48.

The output circuit of the discharge device 20 is conductive only duringthe half cycles when the lower end of transformer secondary winding I6is positive with respect to its upperend. The output circuit may betraced from the lower end of secondary winding l6 through a conductor50, relay winding 46, a conductor 5|, anode 4|, cathode 43, a conductor52, biasing resistor 53 and its associated parallel by-pass condenser54, and a conductor 55 to the upper terminal of transformer secondarywinding I6.

The input circuit of discharge device 40 comprises various branchcircuits which connect cathode 43 and control electrode 42. Oneof thesebranches is efiective to maintain control electrode 42 at a potentialsufiiciently negative with'respect to that of cathode 43 that thecurrent flowing in the output circuit of discharge device 40 is toosmall to energize relay 45 enough to make contact between switch arm 41and contact 48. This branch circuit, hereinafter referred to as thenegative biasing branch may be traced from cathode 43 through conductor52, biasing resistor 53 and its associated parallel by-pass condenser54, conductor 55, variable resistance 56, a conductor 51, and resistor60 to control electrode 42. In this negative biasing branch, controlelectrode 42 is at substantially the same potential as the negative(upper) terminal of transformer secondary l6 during the half-cycles whenthe discharge device 40 is conductive, while oathode 43 is at asubstantially more positive potential, due to the drop across biasingresistor 53.

A second branch of the input circuit is provided which shunts the majorportion bf the negative biasing branch just traced, and when completedmaintains the control electrode 42 at substantially the same potentialas the cathode 43. When'the second branch is complete, the dischargedevice 40 conducts suflicient current to energize relay 45 and causeengagement of switch arm 41 with contact 48. This second branch may betraced from cathode 43 through a conductor 6|, combustion responsiveswitch 33, conductors 62 and 63, limit switch 25, a conductor 64,thermostat 20, a conductor 65 and resistor 60 to control electrode 42.

In this second branch of the input circuit, the combustion responsiveswitch 33 is connected in parallel with a timing condenser 66 by meansof a pair of conductors 61 and 68. v

The heater element 44 of discharge device 40 may be supplied with energyfrom any suitable source. For example, in the system shown, it may beconnected to the terminals of transformer secondary winding l1. Theseconnections have been omitted from the drawing for the sake of Operationof Figure 1 When the parts are in the position shown in the drawing, thethermostat 2n is-satisfled. In

other words,it is not calling for operation of the burner motor Ill.Thebonnet temperature or other limiting condition is below thepredetermined limiting value, so that the switch 25 is I perature.

closed. No combustion is taking place in the burner. Hence, the lastchange affecting the combustion responsive switch 33 was a drop intemperature, and the switch arm 34 is therefore separated from thecontact 35. Let it be assumed that the system has been energized for alength of time sufiicient for the heater element 44 to heat the cathode43 to its operating tem- Underthese conditions, the discharge device issubstantially non-conductive, since the control electrode 42 is biasednegatively by means of the negative biasing. branch of the inputcircuit, previously traced. The statement that the which the thermostat20 is exposed now falls,

causingswitch arm 22 to moveinto engagement with contact 23. Thiscompletes the second branch of the input circuit and shunts biasingresistor 53 and its associated parallel by-pass condenser 54 from theoutput circuit of the discharge device 40. This shunt connection may betraced from the cathode 43 through conductor 68, condenser 66,conductors 61 and 63, limit switch 25, conductor 64, contact 23, switcharm 22, bimetallic element 2|, conductors 65 and 51, and variableresistance 56 to conductor 55. When this connection is first completed,the condenser 56 is substantially uncharged so that no potentialdifference exists across its terminals. To this end the condenser 66 maydesirably be shunted by a resistance 66a of suitably high value.Therefore,

' the potential of control electrode 42 is almost the which maybe tracedfrom power supply line l2 7 through a conductor 1!), burner motor 60 andigniter II in parallel, a conductor 1|, switch arm 41, contact 48', anda conductor 12 to power supply line l3.

As soon as the connection through condenser 66 is completed, theintermittent unidirectional flow of current through it tends to build upa potential on its plates. The polarity of this potential is such thatthe plate connected to the cathode is positive with respect to the plateconnected to the control electrode 42. Each half cycle during which thedischarge device 46 is conductive adds a small amount to the charge ofthe plates of condenser 66. The charge on condenser 66 thereforegradually increases, and as it increases the potential of controlelectrode 42 becomes more and more negative with respect to thepotential of cathode 43. As the potential of control electrode 42becomes more negative, the current flow in the output circuit ofdischarge device 40 becomes less, due to the well knowncharacteristicsof such discharge devices. When the potential acrosscondenser 6.6 reaches a critical value, depending upon thecharacteristic of the discharge device 40, the output current of thedevice 40 is reduced to a point where it is no longer sufiicient tomaintain the energization of relay 45. When the current through winding46 falls to this low value, switch arm 41 drops away from contact 48,thereby deenergizing motor In.

The period of time necessary to charge condenser 66 to its criticalvalue, and thereby cut off operation of the burner motor l0, may bedetermined by adjustment of the variable resister 56. During thealternate half cycles when the condenser 66 is not being charged by theflow of current-through the discharge device 40,

as the value of variable resistance 56 i reduced,-

the period of time necessary to build the charge on condenser 66 up tothe point where it will cause deenergization of relay 25, is increased.

The variable resistance .56 is adjusted so that the period of timeneeded to charge condenser 66 is somewhat longer than the time requiredby the combustion responsive switch 33 to close its contacts followingthe appearance of a flame at the burner. Therefore, under normalconditions, combustion responsive switch 33 will close due to thepresence of the burner flame :before the condenser 66 has chargedsuificiently to cause deenergization of relay 45. As soon as thecombustion responsive switch closes, it shunts the condenser 66, therebyremoving the condenser from any further control of the discharge device40. The burner motor In and the igniter ll wi11 cally. It is onlynecessary to close the switch 66b momentarily in order to dischargecondenser 66 completely. This returns the circuit to its normalcondition, and allows a new starting period to begin.

A normally closed push button switch might be placed in conductor 63 or64 in lieu of switch 661). It would be necessary, in using such aswitch, to hold it open long enough for condenser 66-to dischargethrough resistor 66a.

Figure 2 I Figure 2 discloses a modification of our invention whereinadifferent type of combustion responsive device is employed, and whereina difierent arrangement is used for adjusting the length of the startingperiod of the system. All elements in the circuit of Figure 2 whichcorrespond exactly to elements in the circuit of Figure 1 have beengiven the same reference numerals, and will not, be further described.

In Figure 2, the combustion responsive switch 33 of Figure 1 has beenremoved. In its place,

conductor 6| is connected to the metallic structure of the burner 36,and the conductor 62 has been connected to an electrode 31 mounted in avposition so that it operatively engages the flame therefore remainenergized until the thermostat 20 again becomes satisfied and opens itscontacts. Opening of the limit switch 25 or of the combustion responsiveswitch 33 will also cause deenergization of the system.

The resistance 66a is.provided to insure that the condenser 66 will bein a completely discharged condition when the thermostat 20 closes itscontacts. If the condenser 66 had an initial charge when the thermostat20 called for heat, it can readily be seen that the charging time of thecondenser would be affected thereby. If the polarity of the charge wassuch that the left hand plate of condenser66 was negative, the

charging time would be shortened, and the relay might be deenergizedbefore the combustion responsive switch 33 closed. This wouldeffectively prevent the burner from operating. The

resistance 66a. may desirably .be made ten timesas large as resistance56, in order that its effect on the charging time of condenser 66 willbe small as compared with that of resistance 56.

An initial negative charge having the undesirable efiect mentioned mightoccur, if resistance 66a were not used, in various ways. For example,if, shortly after a call for heat by thermostat 26,

i and before closure of switch 33, the thermostat vided in order thatthe burner-may be started after it has shut down due to charging ofdenser 66 during an attempt to start automatiof the burner 36. Since itis well known that flames are electrically conductive, it will beapparent that as soon as a name appears at the burner, the timingcondenser will be shunted sufficiently so that it cannot charge to apoint where it will cause deenergization of relay 45.

, The variable resistance 56 of Figure 1 has been replaced by a fixedresistance 58 in Figure 2, and the condenser 66 of Figure 1 has beenreplaced by a variable condenser 69 in Figure 2. It will be readilyunderstood that the time necessary to charge condenser 69 may becontrolled by varying its capacitance just as easily as it may becontrolled by varying a resistance connected in circuit with it.

The operation of the circuit shown in Figure 2 is entirely analogous tothe operation of the circuit in Figure 1. It will not therefore befurther described.

It should be-apparent from the preceding description that we haveprovided a burner control circuit in which the timing arrangement isconsiderably simplified over the devices of the prior art. Furthermore,since all the condition responsive controls are connected in the inputcircuit of an electrical discharge device, the current flowing throughtheir contacts is substantially negligi'ble. There is therefore nopossibility of arcing or corrosion at the contacts such as is sometimesencountered in burner control circuits of the prior art.

While we have shown and described preferred embodiments of ourinvention, it will be readily understood that various modifications willsug gest themselves to those skilled in the art. It is therefore ourintention that the scope of our. invention is to be limited only by theappended claims.

We claim as our invention:

1. A control system for a fiuid' fuel burner comprising in combination,a relay controlling the operation of said burner, an electric dischargedevice having an input circuit and an output circuit, a source ofelectrical energy, means connecting said output circuit, said source,and said relay, means for biasing said input circuit so as to hold thecurrent in said output circuit below the value necessary to energizesaid relay, 2. control device for initiating operation of said burner,

a condenser, means including said control device for connecting saidcondenser in said input circuit so that the charging current of saidcondenser opposes said biasing means for a predetermined time, therebypermitting the current in the output circuit to rise above the valuenecessary to energize said relay, and means responsive only to thepresence of a flame at said burner for shunting said condenser so as tomaintain said output current above said value.

, 2. In a control system for a fluid fuel burner,

in combination, means for supplying fuel to said burner, control meansfor said fuel supply means including an electric discharge device havingan input circuit and an output circuit, said control means beingefiective to operate said fuel supply meanswhen said discharge device isconductive and to stop operation of said fuel supply means when saiddischarge device is substantially nonconductive, said input circuitincluding a first connection for maintaining said discharge devicesubstantially non-conductive and a second connection adapted, upon theoccurrence of a current flow therethrough, to overcome the efiect ofsaid first connection and maintain said discharge device conductive,switch means in said second connection for permitting a current flowtherethrough, said switch means being responsive to a conditionindicative of the need for operation of said burner, a condenserconnected in series with said switch means so as to permit a flow ofcharging current to said condenser through said second connection for apredetermined time after closure of said switch, and means responsive tothe presence of a flame at said burner for shunting said condenser.

4. In a controlsystem for a fluid fuel burner, in combination, means forsupplying fuel to said burner, control means for said fuel supply meansincluding an electric discharge device having an input circuit and anoutput circuit, said control means being effective to operate said fuelsupply means when said discharge device is conductive and to stopoperation of said fuel supply means when said discharge device issubstantially nonconductive, and means for controlling the conductivityof said discharge device, comprising a sensitive switching deviceresponsive to a condition indicative of the need for operation of saidburner connected in series with aparallel group including a condenserand a device for completing a shunt circuit around said condenser inresponse to the presence of flame at said burner.

5. A system for controlling the temperature in a space, comprising incombination, a fluid fuel stop operation of said fuel supply means whensaid discharge device is substantially non-conductive, and means in saidinput circuit for controlling the conductivity of said discharge deviceincluding a thermostatic switch responsive to the temperature in saidspace connected in series with a parallel group comprising a condenserand a device for completing a shunt circuit around said condenser inresponse to the presence of a flame at said burner.

6. A ystem for controlling the temperature in a space comprising incombination, a fluid fuel burner, means for supplying fuel to saidburner,

control means for said fuel supply means includdevice for completing ashunt circuit around said condenser in response to the presence of aflame at said burner.

7. A safety control system for apparatus normally operable whenenergized to establish'a predetermined condition, comprising incombina-. tion, an'electric discharge device having an input circuit andan output circuit, a source of elec? trical energy, means connectingsaid output circuit, said source, and said apparatus, means for biasingsaicl input circuit so as to hold the current in said output circuitbelow the value necessary to energize said apparatus, control means forinitiating operation of said apparatuaa condenser, means including saidcontrol means for connecting said condenser in said input circuit sothat the charging current of said condenser opposes said biasing meansfor a predetermined time, thereby permitting the current in the outputcircuit to rise above the value necessary to energize said apparatus,and means responsive to the establishment of said predeterminedcondition for shunting said condenser so as to maintain said outputcurrent abovesaid value.

8. In a safety control system for apparatus nor-.

mally operable when energized to establish a predetermined condition, incombination, means including an electric discharge device forcontrolling said-apparatus so that said apparatus is enr ergized onlywhen said device is conductive,

means responsive to a condition indicative of the need for operation ofsaid device in its active sense for operatingsaid' control means, meansincluding a condenser in the input circuit of said discharge device formaintaining conductivity thereof for a predetermined time following acall for operation by said condition responsive means, and meansresponsive to the establishment of said predetermined condition forshunting said condenser so as to maintain conductivity of said dischargedevice.

9. A control system for an electrically operated device including anelectric discharge device having an anode, a cathode and a. controlelectrode, means for maintaining said cathode in a continually heatedcondition, means for continually impressing a voltage across said anodeand cathode, a relay responsive to the current flow through saiddischarge device for initiating operation of said electrically operateddevice, means for normally biasing said control electrode so that. thecurrent flow through said relay is inadequate to energize said relay,means including,

a condition responsive device for rendering said previously namedbiasing means ineifective and for producing a further biasing voltage onsaidcontrol electrode at a predetermined'rate so that after apredetermined time delay a lowering of current flowing through saiddischarge device to a predetermined value will cause said electricallyoperated device to be deenergized, and means responsive to apredetermined normal condition of operation of said electricallyoperated device for overcoming said further :biasing voltage so thatsaid electrically operated device will remain energized when saidpredetermined normal condition of operation obtains before theexpiration Y of said predetermined time delay.

10. In a burner control system, a relay for controlling the flow of fuelto a burner, means for controlling the energization of said relay, saidmeans including an electric discharge device having an anode, a cathodeand a control electrode,

means for impressing a voltage across said anode and cathode, meansincluding a condition responsive devicefor controlling said electricdischarge device to efiect current flow therethrough and I through saidrelay, a condenser connected in setrolling a burner, an electronicdischarge device said output terminals of said discharge device,

means for applying to said input terminals a biasing voltage of suchmagnitude as to hold the current in said output circuit below the valuenecessary to energize said relay,

a condenser, and connections between said condenser and said inputterminals adapted to include a control switch, said connection beingefiective'when completed by said control switch to cause charging ofsaid condenser and to oppose'said biasing voltage during the time saidcondenser is charging, thereby permitting the current in the outputcircuit to rise above the value necessary to energize said relay. andconnections adapted when completed to include mean responsive to thepresence of a burner flame and effective when completed and upon theoccurrence of a flame to shunt said condenser so as to maintain saidoutput current above said value. 20

12. In apparatus for controlling a fluid fuel burner, a relay adapted tobe employed for controlling a burner, an electronic discharge device forcontrolling the energization of said relay, said device having an anode,a cathode and a control electrode, means for impressing a voltage acrosssaid anode and cathode, mean for controlling said electric dischargedevice to eiIect current i ow therethrough and through saidreIay, acondenser, connections from said condenser adapted to be connected to acondition responsive device andjbeing eilective when connected tocondition responsive device to produce a biasing voltage on said controlelectrode at apredetermined rate so that after a predetermined timedelay a lowering of current flowing discharge device to a predeterminedvalue .will cause said relay to be deenergized, andifurther connectionsadapted when completed to include having input and output terminals,means for employing electrical energy to said apparatus, an outputcircuitfor said discharge device including said energy supplying means,said relay, and

means responsive to the presence 01' combustion and efle'ctive whencompleted and upon the oc- I currence of a flame to'discharge saidcondenser so that said relay will remain energized when combustionoccurs before the expirationof said predetermined time delay.,

' CHARLES B. SPANGENZBERG.

ARTHUR H. SWANSON.

sucha' through said

